diff --git a/app/Dockerfile b/app/Dockerfile
index dc3de69..ccff272 100644
--- a/app/Dockerfile
+++ b/app/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.9
+FROM alpine:3.22@sha256:4b7ce07002c69e8f3d704a9c5d6fd3053be500b7f1c69fc0d80990c2ad8dd412
 ADD app /
 ADD index.html.tmpl /
 EXPOSE 80